Photosensitive materials which have heretofore been used in photosensitive members for electrophotography (hereinafter also referred to simply as "photosensitive members") include inorganic photoconductive substances such as selenium and selenium alloys, dispersions of inorganic photoconductive substances such as zinc oxide and cadmium sulfide in resin binders, organic photoconductive substances such as poly-N-vinylcarbazole and polyvinylanthracene, dispersions of organic photoconductive substances such as phthalocyanine compounds and bisazo compounds in resin binders, and films of organic photoconductive substances as mentioned above, deposited through vacuum evaporation.
Photosensitive members, which are required to have a function of retaining a surface electric charge in the dark, a function of generating an electric charge upon receiving light, and a function of transporting an electric charge upon receiving light, include so-called single layer type photosensitive members comprising one layer having all of these functions, and so-called laminate type photosensitive members with laminated layers respectively having separate functions, one layer of which mainly contributes to generation of an electric charge, and another layer of which contributes to retention of a surface electric charge in the dark and transportation of an electric charge upon receiving light. For example, a Carlson system can be applied to image formation according to the electrophotography method using one of these photosensitive members. The process of image formation according to this system comprises the step of charging a photosensitive member by corona discharge in the dark, the step of exposing the surface of the charged photosensitive member to light to form an electrostatic latent image corresponding to a letter and/or a picture on a copy or manuscript, the step of developing the formed electrostatic latent image with a toner, and the step of transferring the developed toner image to a support such as a paper sheet to fix the toner image onto the support. The photosensitive member from which the toner image was transferred to the support is subjected to removal of the electric charge, removal of the remaining toner, and removal of the electric with light to be ready for reuse.
Photosensitive members for electrophotography wherein use is made of an organic material have recently been put into practical use by virtue of flexibility, thermal stability and a film forming capacity of the organic material. Such photosensitive members include a photosensitive member comprising poly-N-vinylcarbazole and 2, 4, 7-trinitrofluoren-9-on (disclosed in U.S. Pat. No. 3,484,237), a photosensitive member comprising an organic pigment as the main component (disclosed in Japanese Patent Application Laid-Open No. 37,543/1972), and a photosensitive member comprising as the main component a eutectic complex composed of a dye and a resin (disclosed in Japanese Patent Application Laid-Open No. 10,785/1972). Further, a large number of photosensitive members wherein use is made of a hydrazone compound, an oxazole compound, or the like have been reported.
As described above, organic materials have many advantages with which inorganic materials are not endowed. However, the fact has been that there have been available no organic materials sufficiently satisfying all the characteristics required of photosensitive members for electrophotography, among which photosensitivity and characteristics in repeated continuals use have been particularly problematic.